Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!mit-eddie!mit-amt!mlj
From: mlj@mit-amt.MEDIA.MIT.EDU (Mary Lou Jepsen)
Newsgroups: sci.electronics
Subject: Re: Question about LCDs
Message-ID: <2856@mit-amt.MEDIA.MIT.EDU>
Date: 30 Jul 88 19:25:31 GMT
References: <1240@gmu90x.UUCP>
Organization: MIT Media Lab, Cambridge, MA
Lines: 56

In article <1240@gmu90x.UUCP>, dana@gmu90x.UUCP (J Dana Eckart) writes:

> This also means that the nearest pixel is also .012" away.  Do these figures 
> fall into realm of possibility?  If not, what's the highest resolution one
> could hope for with this method given current technology?  The above numbers
> give about 85 pixels/inch.  How many pixels/inch could using layered panels
> give (using current technology)?
> 
> I feel certain that I must be overlooking something rather obvious, otherwise
> wouldn't this have already been done?  I am curious about what it is that I 
> must have overlooked.  I welcome any comments.

I thnk that you might have overlooked some things, but there might be
a way to eliminate the problems that I see:

	1.  Liquid Crystal are normally deposited in sheets of large
area; not into individual small pixels.  It is necessary to align
liquid crystal molecules, this is easier to do if it you have a thin
film, rather then a pit for a blob of crystals and then a lot of space and
then another pit for the crystals...  And, it is especailly difficult
to align the super-twisted nematic liquid crystals.  

	2.  So then you say, ok, let's use four homogeneous layers of
crystals; none of this pit'o'crystals then open space then
pit'o'crystals stuff.  You, of course, plan on using etched
transparent lines of ITO (Indium tin oxide -- a transparent
conductor)so that you don't obstruct the view of layers further away
from the ITO lines.  The problem is that an ITO line carrying information
intended for a pixel either instead or also, "turns on" the area of
the sheet of liquid crystals above the ITO line.

	3.  To solve this problem you further complicate the already
complex design,  you etch your lines while keeping you pixel areas
covered (with photoresist or something) then you fill this area with
indexed-matched optical epoxy (Norland makes some good stuff) and take
out the photoresist with something that won't damage the epoxy
(acetone won't work -- but there is probably something).  Then you
need to fill the areas left with a conductor that is the opposite color of
the activated crystal (black or white depending of the kind of
crystal).  I think that this will work.  Hopefully,  you could fit a
CCD array in this area underneath the active liquid crystal area.
That would yield greater contrast. 


	3. Check the SID digests (Society For Information Display)
their conferences always feature the most up-to-date info.  I think
that the spacing problem hasn't been deemed as important as the
resolution and contrast problems.  Therefore it hasn't been addressed
in the detail that the other problems have.  It sounds like a good way
to me though.  I think that you should pursue it (but it is four times
as expensive as a solution that would simply reduce the spacing
requirement between the pixels ).


Mary Lou Jepsen
mlj@media-lab.media.mit.edu